Dynamic Constitutive Model For Saturated Loess And Deformation Analysis For Soil Around Subway Tunnel

Due to long term cyclic load imposed by running metros, subway tunnel and surrounding soil always suffer from settlement, differential settlement and other induced problems. In the near future, a certain scale construction of urban railroad transportation will be completed in the loessal region of the western China. Most part of Xi’an No.2metro line is beneath watertable where saturated loess exhibits poor mechanical properties. Therefore, the influence of metro-induced load on long term ground deformation should be paid enough attention. Existing dynamic constitutive models rarely pay attention to structure and anisotropy of saturated loess as well as metro induced cyclic load. In the present work, all these factors are considered simultaneously and a new dynamic bounding surface constitutive model is established and is applied to ground settlement analysis. Major achievements of present work are given as follows:(1) Two structural factors are introduced as isotropic structural factor Di and anisotropic structural factor Dr. It is considered that frictional structural damage affects both anisotropic tensor and slope of critical state line of bounding surface. So, a new corresponding rotation hardening principle is raised. Meanwhile, isotropic hardening principle considering the effect of isotropic structural factor Di is quoted, which was established in former studies.(2) A new kinematic hardening principle of mapping center is established by considering the resultant influence of cyclic property and the first two hardening properties. In this principle, mapping center is supposed to switch to inverted stress point when loading direction is reversed and move along with former hardening process of bounding surface.Based on Dafalias bounding surface model and above established hardening principles, a new dynamic constitutive model for saturated loess considering effect of anisotropy, structure and cycling dynamic propertiesit is established. All model parameters are classified, physical signification of each parameter is described in detail, and their determination method are given.(3) The proposed constitutive model is programmed into UMAT-Subroutine. Based on ABAQUS Finite Element Software, static and dynamic triaxial test processes are simulated. The approximately coincidence of simulation results with real test results can deduced that the proposed constitutive model and the UM AT-Subroutine is reasonable.(4) Based on above UMAT-Subroutine and the established intermittent cyclic load model, and considering relationship between pore pressure dissipation and ground settlement, a2-D finite element model for load-tunnel-saturated loess is established. Long term ground settlement pattern and its influence factor in saturated loess region under subway cyclic load are analyzed, and long term settlement range, degree and stable time are predicted.